Embodiments of the present invention relate to an electrostatic chuck for holding a substrate in a process chamber
In the processing of substrates, such as semiconducting wafers and displays, the substrate is placed on a support in a process chamber and suitable processing conditions are maintained in the chamber. The support can include an electrostatic chuck that has an electrode capable of being electrically biased to hold the substrate on the support. The electrode may also be electrically biased, for example with an RF bias power, to energize a process gas in the chamber to process the substrate. The support can also comprise a pedestal that supports the electrostatic chuck in the chamber, and may be capable of raising or lowering the height of the electrostatic chuck and substrate. The pedestal can also provide a protective enclosure for connecting wires, gas tubes etc, that connect to portions of the support.
In a typical chamber process, energized gases are used to process substrates by, for example, etching or depositing material on the substrate, or to clean surfaces in the chamber. These energized gases can comprise highly corrosive species, such as chemical etchants, as well as energized ionic and radical species that can erode away portions of the support, such as an electrostatic chuck composed of aluminum nitride. The eroded support can be problematic because the damaged support may not provide the desired electrical characteristics for processing substrates or holding substrates on the support. Also, particles that have eroded from the support can contaminate substrates being held on the support.
An example of a conventional support having improved resistance to erosion comprises an electrostatic chuck made of a ceramic, such as aluminum nitride, and having an embedded electrode that is brazed to an underlying stainless steel pedestal, as described in U.S. Pat. No. 6,563,686 to Tsai et al, filed on Mar. 19, 2001 and commonly assigned to Applied Materials, which is herein incorporated by reference in its entirety. Electrostatic chucks made of ceramics are desirable because they have improved resistance to corrosion by energized process gases, and can maintain their structural integrity even at high substrate processing temperatures exceeding several hundred degrees centigrade. However, a problem with conventional supports is that thermal expansion mismatch can occur between the ceramic electrostatic chuck and the supporting pedestal, especially during substrate processes conducted at high temperatures. The difference in thermal expansion coefficients of ceramic materials and the metal pedestal materials can result in thermal and mechanical stresses that can cause the ceramic to fracture or chip.
One solution to the thermal expansion mismatch problem is described in U.S. Pat. No. 6,490,146, entitled “Electrostatic chuck bonded to base with a bond layer and method”, to Shamouilian et al, filed on May 7, 1999, and commonly assigned to Applied Materials, Inc, which is herein incorporated by reference in its entirety. The support described by Shamouilian et al. has a ceramic electrostatic member having an electrode that is attached to a base beneath the electrostatic member. The base is made of a composite of a ceramic and a metal that has a coefficient of thermal expansion that is sufficiently close to that of the electrostatic member to reduce thermal expansion stresses, for example, a difference of less than 10%. The ceramic electrostatic member and base are typically brazed together to provide a strong bond between the electrostatic member and base. The base can be secured in the chamber by attaching the base to an underlying support via a metal bond layer.
However, even these advanced substrate supports can eventually require replacement or refurbishment when they erode or have accumulated process deposits that require extensive cleaning after exposure to multiple plasma processing cycles. Sometimes, the entire support has to be replaced, so that a substrate will not become contaminated by flaked particles of process residue or that arise from damaged portions of support, and to ensure that the desired electrical properties of the support are maintained consistent. The replacement of the entire support can be both costly and wasteful. For example, a replacement substrate support can cost tens of thousands of U.S. dollars, and the support may need to be replaced, on average, after the processing of 50,000 to 100,000 substrates, increasing processing costs. The support may also need to be replaced if misuse or accidental operation damages the support surface or edges.
Thus, it is desirable to have a substrate support that exhibits reduced thermal expansion mismatch problems. It is furthermore desirable to have a substrate support that does not require replacement of the entire support as frequently as conventional supports. It is also desirable to have a substrate support that does not incur replacement costs that are as high as those of conventional supports.